Tree descriptions based on dominance constraints are popular in several areas of computational linguistics including syntax,
semantics, and discourse. Tree descriptions in the language of context
unification have attracted some interest in unification and rewriting
theory. Recently, dominance constraints and context unification
have both been used in different underspecified approaches to the semantics
of scope, parallelism, and their interaction. This raises the
question whether both description languages are related. In this
paper, we show for a first time that dominance constraints can be
expressed in context unification. We
also prove that dominance constraints extended with parallelism
constraints are equal in expressive power to context unification.